Applied Anatomy and Physiology

Cardiac control recap

Venous Return Venous Return (VR) is the transport of blood from the capilleries through venules, veins back to the right atrium of the heart. At rest, VR is maintained by blood pressure and the structure of the veins.

Venous Return During Exercise During exercise, the pressure of the blood in the veins is too low to maintain VR, and SV and Q therefore decrease. The body needs extra help to push the blood against gravity through the veins to increase VR and SV.

Venous Return is Supported by… Muscle Pump Pocket Valves Respiratory Pump Smooth Muscle Gravity

VR Mechanisms - Pocket Valves These are valves in the veins to prevent backflow of blood and direct it towards the heart.

VR Mechanisms – Muscle Pump Veins are situated between skeletal muscles. When the muscles contract, this helps to push or squeeze blood back to the heart. http://www.youtube.com/watch?v=HNuPWdfjDoc

VR Mechanisms – Respiratory Pump During exercise, breathing becomes deeper and faster. This causes pressure changes in the thorax and abdomen, squeezing large veins and thus blood back to the heart.

VR Mechanisms – Smooth Muscle Contraction and relaxation of smooth muscle in the middle layer of the vein walls also help push the blood through the veins and towards the heart from the heart.

VR Mechanisms – Gravity Blood from the upper body is aided by gravity as it descends from the heart.

Blood Pooling VR requires a force to push the blood back towards the heart. If there isn’t enough pressure, the blood will sit in the pocket valves of the veins This is called blood pooling, and is often associated with the feeling of heavy legs.

Starlings Law A decrease in Venous Return = A decrease in stroke volume, which = a decrease in Q And An increase in Venous Return = An increase in stroke volume, which = an increase in Q

Starlings Law Starlings Law suggests that stroke volume can increase in response to blood filling the heart It is therefore dependent on venous return Stroke Volume can also increase due to greater contractions of the cardiac muscles during exercise.

VR and Quality of Performance VR is important to performance because it affects SV and Q! Remember Starling’s Law! What would happen if VR is reduced? How would it affect sporting performance?

Reduction in SV / Q decreases blood / O2 to the working muscles Performance is reduced - muscles fatigue if they continue without O2 Good VR will speed up recovery and allow performers to work anaerobically for longer!

Describe how this assists Venous Return! Venous Return Mechanisms Respiratory Pump Pocket Valves Smooth Muscle Gravity Muscle Pump Describe how this assists Venous Return!

Feinting!!! http://www.youtube.com/watch?v= x_-eDv7qSrc&feature=related Watch the following cycling clip of Victoria Pendleton. As she gets faster, can you discuss what is happening to her Q? Finally, if she physically stopped immediately after the race, she may feint. What happens, step-by- step, in this process?

Cyclist Stops Moving (standing) Blood pooling occurs in the pocket valves of the legs Not enough pressure from gravity to supply venous return By stopping, muscle pump and respiratory pump deactivated Venous Return decreases = Q decreases = SV lowers – this reduces blood pressure + creates feinting!